Bone fastener

ABSTRACT

A bone fastener including an expandable member having an axial channel and an elongated element insertable into the axial channel is described. The expandable member is configured to be insertible into a bore drilled in bone. The distal end of the expandable member also may include a structure for axially releasing the expandable member from an emplacement device that places the expandable member into a bone opening. In one embodiment, the structure for axially releasing includes a frangible membrane capable of being severed from the expandable member during emplacement of the expandable member in a bone opening. 
     A rivet for coupling an object to bone for use with an expandable member is also described. The distal end of the elongated element is shaped into a radially projecting portion adapted for engagement with a washer that contacts the object to be coupled. The washer, having upper and lower surfaces and a bore defined between the surfaces, is disposed around a portion of the shaft. The elongated element is adapted for movement independent of the washer since the radial projection of the element has a different radius of curvature than the washer. 
     An apparatus for use within an endoscope is described. The apparatus includes an elongated, substantially hollow holding means for emplacing a bone fastener of the invention in a bone opening. The expandable member includes a structure for axially releasing the expandable member from the holding means. A method of attaching soft tissue to bone is also described. The invention also includes a surgical fastener kit.

BACKGROUND OF THE INVENTION

This application is a divisional of U.S. application Ser. No. 08/163,130filed Dec. 6, 1993 now U.S. Pat. No. 5,725,529 which is acontinuation-in-part of U.S. application Ser. No. 07/765,445, filed Sep.25, 1991, to be issued as U.S. Pat. No. 5,268,001 on Dec. 7, 1993, whichis a continuation-in-part of U.S. patent application Ser. No.07/588,025, filed Sep. 25, 1990, now abandoned; the entire contents ofthese applications are incorporated herein by reference.

A variety of techniques are available for affixing objects such as softtissue to bone. The oldest technique utilizes thread passed through thebone and the tissue to sew the tissue down to the bone. Many sizes,shapes and types of suture and suture needles are available toaccomplish this task. Today, this method is still used for repair oftendons and ligaments in older osteoarthritic patients, although passinga suture through bone is generally difficult and tedious.

Soft tissue repairs also have been accomplished with metal screws orstaples that attach soft tissue to bone. Metal screws and/or staplesare, however, subject to corrosion and consequent loss of structure.Moreover, the presence of metal in an anatomical site can interfere withimaging and diagnostic or therapeutic treatments near the site. Forexample, any metal implants may have to be removed by surgery prior tomagnetic resonance imaging. Patient sensitivity to nickel ions andstainless steel implants has fueled a growing controversy regarding theuse of materials containing high quantities of nickel includingnickel-titanium alloys such as Nitinol. Also, it is almost impossible toadjust the compression exerted by screws and staples on soft tissue.Thus, these devices are not fully satisfactory for soft tissue repair.

Other devices employ a suture anchor installation affixed to an arc ofwire or a plurality of barbs disposed on an outer surface of the sutureanchor body. The barbs or arc of wire are set by applying traction tothe suture. Unfortunately, it is not always possible to position theanchor at a precise location within a bone if an anchor is being drawnupwards in a bone hole by applying tension to a suture. Furthermore,many of the fastening devices require some type of impact or impulse toset the fastener in position. Impact emplacement or setting ofbone/suture anchors may result in injury to the patient as well asplacing unnecessary strain on the bone/suture fastener itself.

SUMMARY OF THE INVENTION

The present invention is directed to a novel apparatus for emplacing abone fastener that eliminates the problems created by conventional bonefastener emplacement devices.

In general, the invention features a bone fastener including anexpandable member having an axial channel and an elongated elementinserted into the axial channel. The expandable member is configured tobe insertible into a bore drilled in bone. The member is expanded usinga continuous, compressive force (i.e., pressure without impulse orimpact). The expandable member is grasped at its distal end throughoutthe emplacement procedure and is axially released from an emplacementtool.

In one embodiment, a fastener for coupling an object to a bone isdescribed. The fastener includes a cylindrical expandable member forinsertion into an opening in a bone, the member including an outersurface for expandable engagement with an inner surface of the boneopening. An axial channel is defined in the expandable member, thechannel extending at least partially between proximal and distal ends ofsaid expandable member. An elongated, insertion element that iscompressed into the expandable member is also part of the fastener. Theinsertion element has proximal and distal ends and a channel definedbetween the ends for engagement with a suture. Preferably, the insertionelement includes a projection that expands the axial channel of theexpandable member in an ineversible manner to obtain a press-fit withthe bone opening. In preferred embodiments, the outer surface of theexpandable member includes a plurality of projections for engagementwith the inner surface of the bone opening. The distal end of theexpandable member also may include a structure for axially releasing theexpandable member from an emplacement device that places the expandablemember into a bone opening. In one embodiment, the structure for axiallyreleasing includes a frangible membrane capable of being severed fromthe expandable member during emplacement of the expandable member in abone opening.

The invention also pertains to a rivet for coupling an object to bonefor use with an expandable member capable of insertion into an openingin a bone. The rivet includes an elongated insertion element adapted forcompression into a distal end of the expandable member. The insertionelement has a shaft with proximal and distal ends, an outer surface ofsaid shaft including a radially outward projecting portion adapted toexpand the expandable member. The distal end of the elongated insertionelement includes a radially projecting portion adapted for engagementwith a washer that contacts the object to be coupled. The washer, havingupper and lower surfaces and a bore defined between the surfaces, isdisposed around the shaft of the insertin element. The element isadapted for movement independent of the washer since the radialprojection of the insertion element has a different radius of curvaturethan the washer.

The invention further includes the combination of a bone; an openingdefined in the bone and an expandable member inserted into the openingin the bone. The expandable member includes an elongated, insertibleelement, as described above, and further includes at its distal end, atleast pat of a means for axially releasing the expandable member from aholder, the holder for emplacing the expandable member in the boneopening.

In preferred embodiments, the expandable member and insertible elementare formed out of a bioabsorbable polymer such as polylactide,polyglycolide and combinations thereof.

The invention also pertains to an apparatus for use within an endoscope.The apparatus includes an elongated, substantially hollow holding meansfor emplacing a bone fastener in a bone opening, the holding meanshaving distal and proximal ends. An expandable member having a proximalend and a distal end integral with the proximal end of the holding meansis also included. In one embodiment, the expandable member includes astructure for axially releasing the expandable member from the holdingmeans. The structure may be a frangible membrane disposed intermediatethe proximal end of the holding means and the distal end of theexpandable member.

A method of attaching soft tissue to bone is also described. The methodincludes providing an expandable member for insertion into an opening ina bone. The member has defined in it an axial channel having a certaindiameter. The member also includes a structure for axially releasing theexpandable member from a holding means. Next, the expandable member isengaged at a distal end thereof by way of the emplacement means. Theexpandable member is inserted into soft tissue and bone whilemaintaining engagement with the distal end of the expandable member. Acontinuous, compressive force is then applied to the expandable memberto expand the diameter of the axial channel so that an outer surface ofthe expandable member engages with the bone. The structure for axiallyreleasing the expandable member is then activated, so that theexpandable member is released from the emplacement means when thecontinuous force stops.

An apparatus for placing a bone fastener in an opening in a boneincludes the combination of an expandable member with an axial channeldefined therein; an elongated, substantially hollow holder for theexpandable member, an insertion element for engagement with an innersurface of the axial channel; a structure for axially releasing theexpandable member from the holder when the expandable element is fullyexpanded within the bone opening; a structure adapted for co-axialmovement relative to the holder for placing the element into the axialchannel of the expandable member; and a structure co-axially moveablewithin the hollow body for releasing the expandable member from theholder.

The invention also includes a surgical fastener kit. The kit includes anexpandable member for insertion into an opening of the bone, the memberhaving an axial channel defined in it and an outer surface for engagingan inner surface of the bone opening. The kit also includes an elementfor insertion into the axial channel. This element has a projectingsurface for engaging the inner surface of the axial channel. This kitalso includes a holder for engaging with the expandable member, theholder capable of maintaining the expandable member in position with thebone opening. In other embodiments of the kit, a grasper/manipulator forthe suture, a drill and a retrieval device are also included.Preferably, the kit is encased in a sterile tray or other receptacle foruse by an operator at a site.

It is an object of the present invention to provide a bone fastener ofsimple design and construction.

It is another object of the present invention to provide a bone fastenerhaving one or more bioabsorbable components.

It is a further object of the present invention to provide a bonefastener that can be set within a bone hole without requiring the needfor a suture.

It is yet another object of the present invention to provide anapparatus for emplacing a bone fastener that does not require an impactor impulse in order to deploy the fastener and that allows the operatorto adjust the force attaching a tissue to a bone.

It is another object of the present invention to provide a method foremplacing the bone fastener that eliminate the use of nitinol bars orother similar devices.

It is yet another object of the present invention to provide anapparatus for inserting a bone fastener that can be usedarthroscopically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section through the expandable member of the presentinvention;

FIG. 2 is a cross-section through an expandable member of the presentinvention in which the distal end is configured to form a radialprojection;

FIG. 3 is a cross-section through a rivet-type expandable member placedin a bone opening;

FIG. 4 is a cross-section of an insertion element the present invention;

FIG. 5 is a cross-section of another embodiment of an insertion elementof the invention;

FIG. 6 is a perspective view of another embodiment of an insertionelement and washer of the present invention;

FIG. 7 illustrates in a less diagrammatic cross-sectional view, a suturefastener of the invention emplaced in a pre-drilled hole in bone. ThisFigure shows deformation of the outer portion of expandable memberwithin irregularities in the bone hole wall;

FIG. 8 is a cross-section of an embodiment of the bone fastener in whicha proximal projection extends out of the proximal end of the expandablemember;

FIG. 9 is a cross-section of a further embodiment of FIG. 8;

FIG. 10 is a cross-section of an elongated, slidable suture insertionelement of FIG. 5 in place within expandable element in a bone opening;

FIG. 11 is a cross-section illustrating an insertion element rivet andwasher of FIG. 6 in place within expandable element in a bone opening;

FIG. 12 is a diagram showing emplacement of expandable member withinbone hole using a preferred holding means;

FIG. 13 is a cross-section of one embodiment of expandable member andholding means of the invention;

FIG. 14 is a cross-section of another embodiment of an expandable memberand holding means of the invention;

FIG. 15 is a cross-section of a frangible membrane of the invention;

FIG. 16 is a cross-section of another embodiment of a frangible membraneof the invention;

FIG. 17 is a cross-section showing emplacement of a bone fastener withina bone hole using an apparatus of the present invention;

FIG. 18 illustrates one step in the expansion of the expandable memberusing the method and apparatus of the invention;

FIG. 19 shows a second step in the progress of expansion of theexpandable member;

FIG. 20 illustrates an expandable member emplaced in a bone hole and aninsertion element in its full frontward position just after axialrelease from holding means;

FIG. 21 is a cross-section of one type of holding means adapted for usewith an insertion element in the shape of a rivet;

FIG. 22 is a cross-section of another embodiment of the rivet of FIG.21;

FIG. 23 is an exploded view of one embodiment of an emplacementapparatus of the invention;

FIG. 24 is an exploded view of another embodiment of an emplacementapparatus of the invention.

FIG. 25 is a cross-section of another embodiment of an expandable memberand holding means of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The bone fastener, according to the invention, generally includes anelongated insertion element and an approximately cylindrical expandablemember with an axial channel for receiving the insertion element. In itsunexpended state, the expandable member can be placed into a pre-drilledopening in a bone. A diameter of at least a portion of the insertionelement is greater than that of at least a portion of the axial channelso that, when the element is inserted into the axial channel, the widerportion of the insertion element is forced outward against the axialchannel. The axial channel is susceptible to enlargement by this forceacting substantially orthogonal to the axial channel. This outward forcecauses the expandable member to expand ineversibly against the wall ofthe opening, fixing the insertion element within the expandable memberand fixing the expandable member in a pressure fit firmly within theopening. As described in more detail below, the insertion element or theexpandable member, or both of them, can be adapted to provide a fastenerfor attaching soft tissue using a suture or to provide a rivet forattachment without a suture.

A. The Expandable Member

An embodiment of the expandable member 10 of the present invention isillustrated in FIG. 1. The expandable member is a substantiallycylindrical body having one and another ends; a proximal end 12 thatfirst enters the bone opening and a distal end 14 farthest away from theproximal end. The expandable member is preferably constructed of abiocompatible material that is sufficiently deformable so that, whenexpanded within a bone opening, the member will conform to a substantialdegree with the irregularities in the bone opening wall. The term"biocompatible" means that the expandable member material is chemicallyand biologically inert. Suitable materials for the expandable memberinclude, for example, an implant grade high density polyethylene, lowdensity polyethylene (PE 6010 and PE 2030) and polypropylene (13R9A and23M2: all made by Rexene, Dallas, Tex.). Of these, PE 6010 and 13R9Ahave been FDA listed as class 6 materials.

The expandable member may also be bioabsorbable. The term"bioabsorbable" refers to those materials that are meant to bedecomposed or degraded by bodily fluids, such as, for example, blood andlymph. The expandable member is preferably made from a biodegradablepolymer or copolymer of a type selected in accordance with the desireddegradation time. That time in turn depends upon the anticipated healingtime of the tissue which is the subject of the surgical procedure. Knownbioabsorbable polymers and copolymers range in degradation tie fromabout 3 months for polyglycolide to about 48 months forpolyglutamic-co-leucine. A common bioabsorbable polymer used inabsorbable sutures is poly (L-lactide) which has a degradation time ofabout 12 to 18 months. The preferred expandable member is comprised ofan absorbable copolymer derived from glycolic and lactic acids, such asa synthetic polyester chemically similar to other commercially availableglycolide and lactide copolymers. Glycolide and lactide degrade andabsorb in the body by hydrolysis into lactic acid and glycolic acidwhich are then metabolized by the body.

The following Table set forth below lists polymers which are useful forthe bioabsorbable material employed for the expandable member, and otherparts of the bone fastener as described below. These polymers are allbiodegradable into water-soluble, non-toxic materials which can beeliminated by the body. Their safety has been demonstrated and they arelisted as approved materials by the U.S. Food and Drug Administration.

TABLE

Polycaprolactone

Poly (L-lactide)

Poly (DL-lactide)

Polyglycolide

95:5 Poly (DL-lactide-co-glycolide)

90:10 Poly (DL-lactide-co-glycolide)

85:15 Poly (DL-lactide-co-glycolide)

75:25 Poly (DL-lactide-co-glycolide)

50:50 Poly (DL-lactide-co-glycolide)

90:10 Poly (DL-lactide-co-caprolactone)

75:25 Poly (DL-lactide-co-caprolactone)

50:50 Poly (DL-lactide-co-caprolactone)

Polydioxanone

Polyesteramides

Copolyoxalates

Polycarbonates

Poly (glutamic-co-leucine)

Referring to FIG. 1, the expandable member 10 includes an outer surface13 for secured engagement with an inner surface of a bone opening. Outersurface 13 can be smooth or can be provided with a plurality of ridges16 as shown. In particular, a preferred configuration includes aplurality of annular ridges for engaging irregularities in the boneopening wall as the expandable member 10 deforms and conforms to thebone opening wall during and after expansion. It will be appreciatedthat ridges 16 may also be axially aligned with the long axis (shown byarrow A in FIG. 1) of the expandable member. The shape and design of theouter surface ridges 16 are not intended to limit the scope of theinvention in any way.

The ability of the expandable member to conform to the inner dimensionsof a bone opening may be augmented considerably by providing the outersurface of the expandable member with one or more slots (not shown)extending between the proximal and distal ends of the expandable member,the ends of the slots disposed at some distance remote from the proximaland distal ends of the expandable member. That is, the ends of the slotsare not in contact with the ends of the expandable member. The slotsallow the member to flex and conform to irregularities in the bone hole.The slots may be run axially or circumferentially along the outersurface of the expandable member.

An axial channel 18 is defined between the ends 12, 14 of the expandablemember 10 and preferably extends completely through the expandablemember. The axial channel 18 has a certain inner diameter, indicated byreference letter D in FIG. 1. The diameter may be substantially constantalong the longitudinal axis (A) of the axial channel 18, although thediameter may also vary along one or more portions of the length of thechannel. In one embodiment, (illustrated below in FIG. 9) one or moresteps 20 are defined in the inner surface 19 of the axial channel 18.These steps are designed to mate with corresponding ridges on the outersurface of an insertion element (see below).

Referring again to FIG. 1, one end of the expandable member, (i.e. theproximal end 12) is specially adapted for insertion into the boneopening. This end is always of a diameter smaller than the insidediameter of the bone opening. The proximal end 12 of the expandablemember 10 may include a substantially flat portion 21 for engagementwith an outer surface of an insertion element (see FIG. 8).

The expandable member 10 may also be adapted to form a rivet fordirectly affixing soft tissue, or an object such as a bone plate, to thebone at the fixation site. FIG. 2 shows an example of such a rivet 22,in which the distal end 14 of the expandable member is configured toform a radial projection 23. In FIG. 2, the projection is formed as aflange 24. The proximal surface 25 of flange 24 is generally planar andperpendicular to the longitudinal axis (A) of the member 10. The distalsurface 26 of flange 24 is contoured to provide a smooth, generally domeshaped head, thinner near the margin than toward the center.

FIG. 3 illustrates a rivet-type expandable member 10 placed in a boneopening. The member 10 has a distal end 14 configured to form a radialprojection 23 and a stand-off 28. The stand-off 28 is disposed betweenthe radial projection 23 and a bone surface 29. The member 10 may haveon its outer surface 13 a series of ridges 16 over an area that is tocontact a bone opening wall 30 and a smooth section 31 over an areabetween the ridges 16 and the radial projection 23. The outer surface 13of the expandable member 10 may also be provided with a stop 32extending substantially orthogonal to the outer surface 13 of themember. Stop 32 is provided at the junction between the stand-off 28 andthat portion of the outer surface 13 that contacts the bone wall 30 tolimit precisely the depth to which the expandable member is insertedinto the bone opening 33. In the embodiment illustrated, this stop 32 isformed as a pair of substantially rectangular protrusions, extending farenough out from the outer surface 13 of the member so that theprotrusions contact the bone surface 29 at an edge 17 of the boneopening 33, stopping the frontward progress of the expandable member 10.When the operator senses the contact of the stop with the bone surface,a mechanism for inserting an insertion element can be activated, thuseffecting fixation of the expendable member at the pre-determined depth.Stand-off fasteners can be dimensioned to provide for various insertiondepth and stand-offs, according to the particular surgical setting.

FIGS. 1-3 also illustrate a feature of the invention common to manyembodiments of the expandable member; namely a structure 15 for axiallyreleasing the expandable member from a holder device (not shown). Thestructure, described in more detail below, is preferably a membrane thatis broken during emplacement of the bone fastener in a bone opening. Themembrane is broken by a substantially continuous, non-impact force in adirection parallel to (i.e., a to) the longitudinal axis of theexpandable member. Structure 15 is disposed at a distal end of theexpandable member 10 and is represented in FIG. 3 as a jagged, distaledge of projection 23. This is, when fully emplaced in a bone opening33, the expandable member may retain a portion of the previously intact,axially releasing structure 15.

In other embodiments, not illustrated here, the outer surface of theexpandable member can include self-tapping screw threads for engagementwith the inner surface of the bone opening. The screw threads providefor positioning of the expandable member in the hole at its desireddepth or for applying a desired force upon the object between a radialprojection of the expandable member and the bone surface, prior tofixation by forcing the insertion element into the axial channel of theexpandable member. In such a turnable screw thread configuration, theunexpended member can be turned into a bone hole having a diametersomewhat smaller than the outside diameter of the screw threads, so thatthe screw threads self-tap the hole to some extent as the member isturned into the hole. Although the threads are not meant to tap the bonehole to an extent sufficient by themselves to effect fixation of themember, surfaces of the screw threads can be hardened sufficiently tocut or abrade the bone hole wall. Such hardening can be provided, forexample, by forming the member of a relatively deformable polymermaterial that can be hardened by application of heat or radiation, andthen irradiating selective parts of the member outer surface to hardenit at those parts. Ultimately, the softer material of the member can beprovided over selective parts of its surface with a thin coating of aharder more durable material. Once such a self-tapping member has beenturned into the bone hole To the desired depth, an insertion element canbe forced into the a channel of the member, expanding it and deformingthe outer surface thereof as described above.

The expandable member may be fabricated by conventional molding orextrusion procedures and the sizes can vary over a wide range dependingupon the particular surgical procedure. An exemplary expandable membercan be about 0.40 inches (10.1 mm) long, with an outside diameter ofabout 0.140 inches (3.5 mm), the proximal opening of the axial channelbeing tapered to about 0.07 inches (1.7 mm).

B. The Insertion Element

FIG. 4 illustrates in diagrammatic cross-section an insertion element 34of the present invention. The insertion element 34 is a substantiallyelongated shape having distal 35 and proximal 36 ends, and an outersurface 37. The outer surface, most preferably at one end, has aprojection 38 for engagement with inner surface 19 of the axial channel18 of expandable member 10 (see FIG. 1). Insertion element 34 may beconstructed of a relatively hard biocompatible material such that theprojection 38 expands the expandable member outwardly in a directionsubstantially orthogonal to the longitudinal axis of the expandablemember. It will be appreciated that the projection 38 on the outersurface 37 of insertion element 34 can include a variety ofconfigurations and designs. These configurations are not intended tolimit the scope of the invention in any way.

A channel 40 is defined between ends 35, 36 of the insertion element.The channel is adapted to engage a suture. In the embodimentillustrated, channel 40 extends completely between the opposed ends 35,36 of insertion element 34. The insertion element at one of its ends,preferably the proximal end 36, includes a structure for attaching asuture. As illustrated in FIG. 7 below, the structure is most preferablyan outer, flattened, peripheral wall 43 of insertion element 34. Thisouter wall is of sufficient width to engage a knot 44. Other means forattaching a suture may include, for example, one or more slots disposedat an end of the insertion element for trapping the knotted free ends ofthe suture within the jaws of the slot(s). Further, a suture attachingmeans can include a variety of clips or other devices.

The embodiment of FIG. 5 shows insertion element 34 provided with achannel to receive an intermediate portion of a suture (i.e., a segmentbetween the free ends) to form a so-called "slidable" suture element.Insertion element 34 has a generally cylindrical shaft 52 provided withan expanded distal portion 48. A channel 50 is defined through the shaft52 in a direction substantially at right angles to the longitudinal axis(A) of the shaft and may be located anywhere along the shaft.Preferably, the channel 50 is defined at, or adjacent to, the distal end35 of the shaft 52. One or more projections 38 are provided for engagingthe inner surface 19 of the expandable member's axial channel 18 (seeFIG. 1). An intermediate portion of a suture thread may be engagedwithin channel 50. The expanded portion 48 at the distal end 35 of shaft52 may be provided with a plurality of grooves, not shown. These grooveshave a diameter sufficient to receive the suture thread, thus allowingthe suture thread to the flat and substantially parallel to thelongitudinal axis of the insertion element without protruding.

FIG. 10 illustrates the elongated, slidable suture insertion element ofFIG. 5 in place within expandable element 10 in bone opening 33. Allreference numbers are identical to those shown previously. Thisparticular fastener is designed to engage an intermediate portion 47 ofsuture 46.

Another embodiment of an insertion element of the present invention isprovided in FIG. 6 which shows an insertion element 34 in the shape of arivet 58. This rivet is for coupling an object to bone for use with theexpandable member of the invention. Rivet 58 is an elongated element forinsertion into the axial channel 18 of expandable member 10 (see FIG.1), the rivet having a shaft 52 with distal and proximal ends 35, 36,respectively. Rivet 58 may have a channel 40 defined between the ends. Aradial projecting portion 60 is provided at the distal end 35.

A washer 62 having an annular bore 64 may additionally be provided toenclose a portion of the shaft 52. The washer has upper 63 and lower 65surfaces and bore 64 is defined between these surfaces as a singleopening. The shaft 52 of the rivet is inserted within the bore.

The upper surface 63 of washer 62 is in facing relationship, and may beengaged with a lower surface 66 of the radial projection 60. Preferably,as shown in FIG. 6, the lower surface 65 of the washer includes a seriesof spaced-apart projections 67 extending away from the radial projection60 and toward the proximal end 36 of the rivet. Spaced-apart projections67, which may be of variable length, are intended to be inserteddirectly into the bone or into tissue distal to the bone and provide agrasping surface for the washer. The height of spaced-apart projections67 provides sufficient distance between the washer and tissue so thatthe tissue will not undergo necrosis by being compressed too tightly bythe washer or projection 60.

Most preferably, the outer diameter of the radial projection 60 isgreater than the diameter of annular bore 64 of washer 62 whichdiameter, in turn, is greater than the outer diameter of rivet shaft 52.Thus, the bore of the washer is sufficiently large so that the washercan slide underneath the projection 60 of the rivet 58. This alsoprovides sufficient distance between tissue and rivet to eliminate orsubstantially suppress tissue necrosis (see also FIG. 11). Moreover, theupper surface 63 of washer 62 and the lower surface 66 of radialprojection 60 have a different radii of curvature. This differentialradii of curvature allows the rivet to "float" between the tissue andthe washer. It therefore allows the rivet to move relative to the washerto account for different orientations and angles of the bone surface.

FIG. 11 illustrates an insertion element rivet 58 and washer 62 of FIG.6. The rivet is in place within expandable element 10 in bone opening33. FIG. 11 also illustrates how projections 67 are inserted into tissue68 and bone 69 to provide a grasping surface for the washer 62. Allother reference numbers are as previously disclosed. FIG. 1 particularlyillustrates the floating nature of rivet 58 within its captured washer62, allowing insertion in the bone at angles other than exactlyorthogonal to the tissue and/or bone surface.

In further embodiments, one or both of the washer surfaces 63, 65 mayinclude a means for enhancing tissue proliferation on the washer afterit is inserted into the tissue and bone opening. This means forenhancing tissue proliferation can include a plurality of smallapertures (not shown in FIG. 6) defined between the upper and lowersurfaces 63, 65 of the washer 62, these apertures disposed on aperipheral portion of the upper and lower surfaces. Further, tissueproliferation can be enhanced by including one or more roughenedportions (not illustrated) on either, or both, of the upper and lowersurfaces of the washer. The washer and/or insertion member could also becoated or impregnated with a variety of bone and tissue growth enhancingfactors such as, for example, hydroxyapatite, calcium phosphate, and thelike. Preferably, the washer is made of a bioabsorbable materialidentical to those described above. The chemical composition of thewasher may be chosen so that it will be absorbed completely once thetissue fixed by the rivet has reattached itself to the bone. Moreover,the insertion element may also comprise a bioabsorbable material, asdescribed above with regard to the expandable element.

A significant advantage of the rivet configurations of the presentinvention is that the operator can set the compressive force betweentissue, fastener, and bone by manually adjusting the pressure of therivet against the tissue at the time the tissue is being fastened.

FIG. 7 illustrates in a less diagrammatic cross-sectional view, a suturefastener of the invention emplaced in a pre-drilled hole 33 in bone.FIG. 7 shows deformation of the outer portion of expandable member 10within irregularities in the bone hole wall. This deformation resultsfrom the forcible expansion of the expandable member within the bonehole and has two major effects: (i) the density of the bone surroundingthe expandable member is increased by the forces exerted upon the boneand (ii) a bulge is created underneath the outer bone surface causinginterference between the insertion element and the exit diameter of thebone hole.

The insertion element 34 has been compressed into the axial channel 18of an expandable member 10, the proximal projection 38 of the insertionelement 34 expanding the member's outer surfaces 13 thereof against thewall 30 of the bone hole 33. The term "compressed" refers to a forcelacking impact or impulse. The suture 46, which can be, for example, astandard braided dacron suture, is knotted against the proximal end 36of insertion element 34, passes through axial channel 40 and out of thefastener 11 where it can be used to attach soft tissue to the bone atthe fixation site. The severed axial releasing structure 15 is alsoillustrated at distal end 14 of expandable member 10.

FIG. 8 illustrates an embodiment in which proximal projection 38 isplaced so that it extends out of the proximal end 12 of expandablemember 10. In this configuration, a shoulder 168 of proximal projection38 engages flat portion 21 at the proximal end 12 of the expandablemember 10. All reference numbers are identical to those presented above.This engagement provides added security to the bone fastener to preventthe insertion element from backing out of the expandable member.

FIG. 9 illustrates a further embodiment in which a step 20 is defined inthe inner surface 19 of axial channel 18. The step is adapted to matewith a corresponding ridge 39 on the outer surface of insertion element34. Alternate embodiments may include a plurality of steps and ridges aswell. All reference numbers are identical to those presented previously.

The insertion element mates with the axial channel of the expandablemember. Accordingly, its size may also vary over wide limits. Exemplaryinsertion elements designed to mate with the expandable membersdescribed previously are about 0.44 inches (11.1 mm) long with a channeldiameter of about 0.060 inches (1.5 mm). The rivet type insertionelement (see FIG. 6) has a distal radial projection about 0.180 inches(4.6 mm) wide, with a total length of about 0.5 inch (12.7 mm). Anexemplary slidable suture element (see FIG. 5) is about 0.47 inches(11.9 mm) long, with a distal bore about 0.05 inches (1.3 mm) across and0.04 inches (1.0 mm) deep. An exemplary washer designed to mate with therivet of FIG. 6, is about 0.29 inches wide, with a central bore about0.14 inch (3.5 mm)". A total of six projections may be equally spacedaround the lower washer surface, each projection about 0.065 inches (1.6mm) long.

C. Holding Means

FIG. 12 shows emplacement of member 10 within bone hole 33 using apreferred holding means 70 which is adapted to provide for firmdeployment of the fastener without imposing substantial forces upon thebone itself in directions toward or away from the bone. In FIG. 12,expandable member 10 having axial channel 18 and outer surface 13 isshown in an unexpended state at which the axial channel 18 has adiameter (a) and the outer surface 13 has a diameter (b) at its widestpoint or points. Diameter (b) may be equal to the diameter (c) of thebone hole so that expandable member in an unexpended state passes into ahole in a light, press-fit configuration. The holding means 70 is anelongated, substantially hollow tube 71 having an inside diameter (d)greater than the outside diameter (e) of distal end 14 of expandablemember 10.

The proximal end 72 of holding means 70 is integral with the distal end14 of the expandable member 10. The term "integral" refers to a varietyof configurations in which the proximal end of the holding means is inphysical communication with the distal end of the expandable member. Theterm "integral" refers to units made of one piece of material as well ascomponents which may be separate initially but are later joined to forma complete device. En the embodiment of FIG. 12, this physical linkagemay be via a continuous, unbroken surface 73 extending between theholding means 70 and expandable member 10.

Nevertheless, a single, continuous surface is not necessary betweenholding means 70 and member 10. Expandable member 10 may be snap-orpress-fit into position at the proximal end of holding means 70 using avariety of mechanisms. Referring to FIG. 13, the proximal end ofexpandable member 10 is press-fat into a bore 71 defined at proximal end72 of holding means 70. The expandable member 10 may include one or moredetents 74 adapted to engage with corresponding surfaces 76 on theholding means 70.

FIG. 14 illustrates a two-piece holding means 70 having an intermediateend 72 supplied with a series of screw threads 75. A correspondingseries of screw threads 78, designed to mate with threads 75, aredisposed at a second, intermediate end 73.

FIG. 25 illustrates another way of integrating the proximal end ofholding means 70 with expandable member 10. As illustrated, proximal end72 of holding means 70 is provided with a bore 71 having surfaces 76designed to mate with corresponding detents 74 on expandable member 10in a manner allowing expandable member 10 to be spun onto holding means70 or crimped onto holding means 70. All other reference numbers are asdescribed previously. Thus, in FIGS. 12-14 and 25, the expandable member10 is constructed to allow the holding means 70 to maintain engagementwith the expandable member during the steps of emplacement in the bone.

Moreover, each of the embodiments of FIGS. 12-14 and 25 includes astructure for axially releasing the expandable member from the holdingmeans. The manner of activating the axial releasing structure isdescribed below but it will be appreciated that the structure may bearranged as a substantially annular ring or membrane of material. InFIGS. 12-14 and 25, axial releasing structure is a frangible membrane84. The term "frangible" refers to a membrane that is breakable orfragile. In particular, FIG. 12 illustrates frangible membrane 84 as anannular attachment portion connecting holding means 70 and expandablemember 10. FIG. 13 illustrates frangible membrane 84 connected thedistal end of expandable member 10 to a detent 74, the membrane betweendetent 74 and member 10 severable during emplacement of the fastener, asdescribed below. FIG. 14 illustrates frangible membrane 84 disposedbetween distal end 14 of the expandable member 10 and a threaded portion75 of holding means 70.

The axial releasing structure, however, may be other than a completeannulus of frangible material. In FIG. 15, the membrane 84 is a seriesof spokes or webbing 85. In this configuration, only the spokes need bebroken. Alternately, as shown in FIG. 16, the structure for axiallyreleasing the expandable member is a plurality of very attenuatedmembranes 86.

Ah exemplary holding means may have a diameter of between about0.070-0.140 inches (1.7-3.5 mm) and is integral with the expandablemember (see FIG. 12) by way of an annular frangible membrane about0.01-0.02 inches (0.25-0.50 mm) thick.

D. Methods

One method, although by no means the only method, for attaching softtissue to bone will be described below with reference to the rivetfastener of the present invention.

To attached soft tissue to bone, a surgeon takes the sharpened proximalend of a K-wire (manufactured, for example, by Kirschner MedicalCompany) and spears the tissue that is to be attached. The proximal endof the K-wire is then placed over the bone surface at the approximatesite of attachment. The K-wire is then drilled into the bone at thatsite. If the location is where the surgeon wants it, the surgeon thenthreads a cannulated drill of the appropriate size over the K-wire. Ahole is then drilled into the bone using the cannulated drill. Thendrill is then removed, leaving the K-wire in place. The rivet of theinvention is then loaded into an expandable member contained within anemplacement apparatus (described below with reference to FIGS. 23 and24). The rivet is run over the K-wire and the expandable member presseddownwards through the tissue and into the bone hole so that theexpandable member is emplaced into the bone hole. If the surgeon decidesthat the orientation of the bone fastener and soft tissue is correct,the emplacement apparatus is triggered to set the bone fastener withinthe bone hole. The emplacement apparatus and then the K-wire are removedin turn. Other variations on this technique include first drilling abone hole and then punching a hole through the soft tissue. The tissueis then moved over the bone hole using, for example, a K-wire or agrasping device. The K-wire is inserted into the hole in the soft tissueand bone and then the emplacement apparatus of the invention is threadedover the K-wire. The preferred method includes providing an expandablemember for insertion into an opening in the bone, the member havingdefined in it an axial channel with a certain diameter, as describedabove. The expandable member includes a structure for axially releasingit from a holding means. The expandable member is grasped at the distalend using the elongated holding means described previously. Theexpandable member is inserted into a bone opening with the holding meanswhile maintaining contact with the distal end of the expandable member.A compressive force, which may be continuous, is applied to theexpandable member in order to expand the diameter of the axial channelso that an outer surface of the expandable member engages the bone. Theforce is applied by compressing the elongated insertion element into theaxial channel of the expandable member. The projecting portion at anouter surface of the insertion element is engaged with the inner surfaceof the axial channel of the expandable member to exert a forcesubstantially orthogonal to the axial channel. The diameter of the axialchannel expands within the bone opening as the projecting portiontravels proximately within the axial channel. The means for axiallysevering the expandable member is then activated, so that the expandablemember, fully expanded into the bone opening by the inserted element, isreleased from the holding means when the continuous, compressive forcestops. In particular, when the frangible membrane is axially severed,the expandable member is disengaged from its holding means.

It is an important feature of the present invention that the forceneeded to expand the expandable member may be substantially continuousand spread out over time so that the force is not an impulse, as inprior art methods. The expandable member is expanded using theinsertible element with a compressive motion that is axially deliveredin a direction substantially parallel to the longitudinal axis of theinsertion element. Thus, the apparatus for inserting a bone fastenerrequires an advancing drive mechanism which lacks any impact or impulsecharacteristics. In physical terms, it can be considered that the systemof: (i) a bone; (ii) a K-wire to guide a drill to make an opening in thebone; (iii) a bone fastener emplaced over the K-wire in the opening; and(iv) an apparatus for emplacing the bone fastener, comprises a closed,continuous boundary system in which no external forces are applied tothe system such as, for example, by a hammer or impactor.

FIG. 17 shows emplacement of a bone fastener 11 within a bone hole 33using an apparatus of the present invention. The bone surface isindicated as reference number 29. Insertion element 34 has at least oneprojection 38 in facing relationship to a beveled portion 88 along innersurface 19 of axial channel 18. A plunger 90 surrounded by a releasingelement 92 (not shown in FIG. 17) is directed from a first position,where the plunger is remote from insertion element 34, to a secondposition, where the plunger is engaged with the distal end 35 ofinsertion element 34. The plunger and releasing element 92 are coaxiallyaligned within hollow tube 71 of holding means 70. The plunger 90 isthen further urged forward, pressing insertion element 34 before it intothe axial channel 18 of the expandable element 10.

FIGS. 18 and 19 show the progress of expansion of member 10 as theproximal projection 38 of insertion element 34 presses outward againstthe inner surface 19 of axial channel 18. In FIGS. 18 and 19, releasingelement 92 is shown with a proximal shearing surface 93 which may be abeveled blade. Any proximal surface sufficient to shear the frangiblemembrane would be sufficient. Also illustrated in FIGS. 18-19 is asuture 46 whose knot 44 is engaged with the suture attachment means 42at the proximal end of the insertion element 34.

Insertion element 34 is forced frontward to its full extent as shown inFIG. 19. As insertion element 34 approaches its full frontward position,the surface 93 of releasing element 92 approaches, then meets, and thenpasses through the structure for axially releasing expandable member 10(e.g., frangible membrane 84), severing the expandable member 10 fromthe hollow holding means 70, and thereby freeing the fully expanded andfirmly fixed fastener 11 from means 70. It will be appreciated thatelement 92 may have a completely annular distal surface 93 to coincidewith the annular structure of the frangible membrane 84 illustratedabove. If the frangible membrane 84 includes a series ofdiscontinuities, as illustrated above in FIGS. 15-16, then the releasingelement 92 can have shearing surfaces that are also discontinuous.

The holding means 70 is then withdrawn from the site, leaving thefastener in place at the fixation site in the bone.

Alternately, the frangible membrane 84 may be severed without using areleasing element. One embodiment of the invention relies on theinherent resiliency of the frangible membrane and the failure of themembrane during tension and elongation. Referring now to FIG. 20, anexpandable member 10 is shown emplaced in a bone hole and an insertionelement 34 in its full frontward position just after axial release fromholding means 70. If the bone hole 33 is of a depth (E) that issubstantially identical to the length of the expandable member 10, aforce (sold arrow X) will be exerted on membrane 84 in a directionsubstantially parallel to the longitudinal axis of the expandable member(double-headed arrow Y) but in a direction opposite the compressiveforce (solid arrow Z) exerted by the plunger 90 in its coaxial travelwithin the hollow tube 71 of holding means 70. It will be appreciatedthat the magnitude of compressive force Z is substantially equal inmagnitude and opposite in direction to force X. Forces X and Z willactivate the axial releasing structure (e.g., the frangible membrane 84)by forcing it to elongate and stretch in the same direction. At acertain point, when force X is greater than the strength of frangiblemembrane 84, the membrane 84 will fail, thus releasing the expandablemember and insertion element from the holding means. Suture 46 and knot44 are also illustrated. This type of releasing mechanism is dependenton the physical properties of the frangible membrane and the rate ofshear.

The same forces can be obtained by providing the insertion element as arivet 58 as illustrated in FIG. 6. In this case, plunger 90 engages theradial projection 23 of the rivet 58 which is stopped against the bonesurface. This engagement provides the forces necessary to elongate andstretch the frangible membrane to its breaking point.

With regard to embodiments in which the frangible membrane 84 includes aseries of attenuated membranes (see FIGS. 15 and 16), the front-to-reardimension of each of the membranes is sufficiently thick so that it canwithstand the counterforce required to balance the force of urging theinsertion element into the axial channel of the expandable member. Butthe connection of the frangible membrane to the expandable member isthin enough so that, with the insertion element fully inserted and theexpandable member affixed in the bone hole, the emplacement means can berotated about its long axis as indicated by arrow F in FIG. 16, to snapoff the connections 86, freeing the expandable member from the holdingmeans.

FIG. 21 shows a view of one type of holding means 70 adapted for usewith an insertion element 58 in the shape of a rivet. Such an insertionelement and holding means are also described above with reference toFIGS. 6 and 14. The element 58 has an axial channel 40. The generallycylindrical holding means 70 has an inside diameter (d) greater than theoutside diameter of the distal end 14 of expandable member 10, and greatenough to accommodate the diameter of distal projection 38 of insertionelement 34, as described above in FIG. 5. The expandable member 10includes frangible membrane 84. The expandable member 10 passes withoutresistance into a bone hole as described above generally, and the memberis positioned within the hole so that in an externally smooth neckportion 31 projects above the bone surface to provide a stand-offbetween the radial projection 60 of the insertion element and the bonesurface. An annular projection 95 on the neck 31 may retain the washer(not shown) of the rivet insertion element 58, preventing loss of thewasher during insertion of the expandable member into the bone hole. Thebore of the washer is designed to receive the expandable member prior toemplacement of the bone fastener of the invention.

The outer diameter (b) of the insertion element 58 is about the same asor slightly smaller than the inner diameter of the neck portion 31 ofthe expandable member. Outer diameter (b) is larger than the innerdiameter (a) of the axial channel 18 of the expandable member 10 sothat, as the rivet shaft is compressed into the axial channel 18, itpasses without resistance through the neck portion 31 but causes theouter, bone engaging surface 13 to expand outwardly against the wall ofthe bone hole. That is, as the rivet is urged frontward, the radialprojection 38 at its proximal end 36 presses outward against the innersurface 19 of the axial channel.

Moreover, the outer diameter (c) of radial projection is sized tointerfere with the axial releasing structure (e.g., frangible membrane84). When this occurs, the progress of the rivet within the expandablemember 10 is momentarily stopped. Further frontward compression of therivet 58 drives its radial projection 60 through the frangible membrane84 and causes a failure of the frangible membrane portion, effectingseparation of the fully installed rivet from the holding means 70. Then,the holding means 70 can be withdrawn from the site. Preferably, lowersurface 66 of radial projection 60 is provided with an abrupt proximaledge to effect a shearing action. A circular undercut 96 on thefrangible membrane further improves the precision of the separation.Thus, the resulting rivet is anchored firmly in place within the bonehole by intimate contact of the outer surface of the expandable memberwith the bone hole. Further, the material to be fastened by the rivet isconfined about the supported neck portion of the expandable memberbetween the bone surface and the washer of the rivet. As described abovewith regard to FIG. 6, projections 67 on the rivet washer 62 serve tofurther engage the tissue with the fastener system.

The method of inserting an expandable member 10 in the shape of a rivet(as shown in FIG. 3) is substantially identical to the method describedpreviously for the insertion element rivet. Thus, the proximal end 12 ofthe expandable member 10 is contoured to pass easily through tissue. Thedistal, radial projection 23 on the expandable member is attached toholding means 70 by way of a frangible membrane 84, as described above.The membrane may be detached by the methods described previously,thereby freeing the Ally expanded and firmly fixed rivet fastener fromthe holding means. The holding means is then withdrawn, leaving theexpandable member rivet in place at the fixation site of the bone,compressing the attached tissue between the prominal end of the radialprojection and the surface of the bone. An alternate configuration foruse in the rivet described immediately above, includes an annularundercut 98 on an inner surface of the radial projection 23, thisexcavation being just proximal to the frangible membrane 84. Theundercut is formed sufficiently deeply into the material of the radialprojection 23 so that when the frangible membrane is cut or otherwisesevered, an annular fragment is cut free of both the radial projection23 and the expandable member (not shown), and any remaining connectionbetween the radial projection and the expandable member being so thinhas to provide little resistance to simply pulling the holding meansaway from the fixed fastener. All other reference numbers are aspreviously described.

E. Apparatus

A preferred emplacement apparatus of the invention retains the holdingmeans and expandable member prior to emplacement. The emplacementapparatus includes means for pressing the insertion element into theexpandable member and then separating the expandable member from theemplacement apparatus. The fastener assembly can include a disposablecartridge, the cartridge containing the expandable member, insertionelement, holding means, and means for attaching the disposable cartridgeto the apparatus.

FIG. 23 is one embodiment of an emplacement apparatus of the invention.Its operation is best exemplified by reference also to FIGS. 18 and 19.The apparatus 99 includes a cartridge 100 which encloses holding means70 attached by axially releasing membrane 84 to expandable member 10.The cartridge is preloaded with plunger 90 and insertion element 34. Areleasing element 92 (not shown in FIG. 23) is co-axially arrangedaround plunger 90 to activate the axial releasing structure (e.g., severthe membrane 84). The insertion element 34 is positioned with itsproximal projection 36 in facing relationship to distal end 14 of theexpandable member 10. Insertion element 34 is provided with a suture 46.The free ends of the suture pass through the axial channel 40, throughchannel 106 of the plunger 90, and are knotted against the proximal end36 of the insertion element 34. The knot 44 is fully contained withinthe expandable member 10 prior to its emplacement in the bone hole, sothat it cannot interfere with the insertion into the hole.

The cartridge 100 may additionally include a take-up spool 112, forstorage of the free ends of suture 46. When the apparatus is loaded,suture 46 is arranged to pass from the knot in proximal end 36 ofinsertion element 34, through axial channel 40, through a hole inplunger axial channel 106, and over and around spool 112. As theapparatus is withdrawn, leaving the fastener with the suture 46 attachedfixed in place in the bone hole, as described above with reference toFIGS. 18-19, the free ends of the suture 46 pay off from the take-upspool 112.

Cartridge 100 is removably attached to hand-held means for urging theplunger 90 frontward (i.e., towards the bone) with respect to thecartridge. In the configuration of FIG. 23, the hand-held means 120consists of two handle elements 122, 124 slidably engaged to provide acomfortable pistol grip 126 by which handle element 124 can be moved ina front-and-rear direction with respect to the handle element 122 bysqueezing the pistol grip 126. The end 123 of the handle element 122 isadapted for removably mounting the distal end 101 of cartridge 100. Theend 125 of handle element 124 includes a push rod 129 whose proximal end127 abuts the distal end 91 of plunger 90 when the handle elements areassembled and the cartridge 100 is mounted onto end 123 of handleelement 122. Alternatively, an axial bore 130 can be arranged to passrearward through push rod 129 and handle element 124 for conducting thesuture distally from the knot at the proximal end of the expandableelement au the way to the outside.

With the apparatus so assembled, the surgeon grasps the apparatus by thepistol grip, and directs the expandable member to the desired depth intothe predrilled hole in the bone. Then, while holding the apparatus inplace, the surgeon squeezes the grip 126 sliding the handle 124frontward with respect to the handle element 122, as indicated by thearrow 131. The push rod 129 presses against distal end 91 of plunger 90,urging the plunger in a non-impulse fashion towards the holding means70, and thereby: (i) compressing element 34 into the axial channel 18 ofexpandable member 10; (ii) causing the expandable member 10 to expandwithin the bone hole 33; and (iii) causing releasing element 92 to severthe frangible membrane 84 between the expandable member 10 and theholding means 70, leaving the fastener fixed in the bone.

An alternate embodiment is shown in the exploded view of FIG. 24. Allreference numbers are identical to those in FIG. 23, unless notedotherwise. The holding means 70 is connected at its distal end by aquick-connecting interlock 500 with the hand-held means 120 for urging aplunger 90 frontward with respect to the expandable member 10. Theapparatus includes a lock mechanism 142 having a series of slots orteeth 143 for gripping the distal end 144 of holding means 70. A cap 146and cap insert 148 are also provided to co-axially engage the lock 143.An actuator drive rod 150 is positioned within the hand held means andis co-axially arranged with spring 152. The drive rod, connected tohandle 122, is forced against plunger 90, as described above.

Preferably The snap-on interlock is configured as an insertible,spring-loaded connector, in which a distal portion of the holding meansforms the "male" part of the connector and a portion of the hand-heldmeans forms the "female" part. With reference to FIG. 24, a flange 510is situated with a rear surface 512 situated a fixed distance distal tothe frangible membrane 84 connecting the expandable member 10 to theholding means 70. Distal to the flange 510, is a groove 514 having afrontward-facing surface 516 generally perpendicular to the longitudinalaxis of the holding means. The holding means tapers distally from theouter edge of the surface 516. The hand held means is provided with agenerally cylindrical bore for receiving that portion of the holdingmeans situated distal to the flange.

The hand-held means 120 is provided with one or more keepers (not shown)that are moved away from its longitudinal axis by the advancing taper518. The keepers then spring into the groove 514 and lock againstfrontward-facing groove surface 516 when the distal portion of theholding means is correctly positioned within the receiving bore of thehand-held means. The rear-facing surface 512 of the flange 510 contactsa part of the hand-held means adjacent the holding means receiving boreto provide a stop establishing the correct rearward position of theholding means within the hand-held means.

The hand-held means 120 is provided with a plunger 90 that can becontinuously urged proximally with respect to the holding meansreceiving bore along the holding means longitudinal axis. Continuouslyand without impulse, the insertion element is driven toward, and into,the axial channel of the expandable member. The plunger 90 includes ashoulder 520 at its proximal end. An edge of the shoulder provides asharpened surface sufficient to activate the releasing structure bysevering frangible membrane 84.

Preferably, the length of the plunger is fixed in relation to the fixedfront-to-rear distance between the rear surface 512 and the frangiblemembrane connecting the expandable member to the holding means. A stopis provided to limit the extent frontward to which the plunger can beurged within the hand-held means, so that the disengagement of theexpandable member from the holding means is complete at just the pointwhere the plunger has been moved to its proximal limit. This ensuresproper emplacement of the fastener in the bone hole, provided that theholding means is properly mounted in the handle and the user urges theplunger frontward as far as it will go.

The components of the bone fastener of the invention may be included ina surgical fastener kit. An exemplary kit may include an expandablemember of the invention; an insertion element of the invention and aholder for engaging with the expandable member, the holder capable ofmaintaining the expandable member in position with the bone opening.Other embodiments of the kit may include a grasper/manipulator forgrasping free ends of the suture to pass the suture through soft tissue.Such a suture-grasping device is described in commonly assigned andco-pending application Ser. No. 08/097,154, filed Jul. 26, 1993, nowabandoned incorporated herein by reference. A K-wire, drill and drillguide may also be also included. Preferably, the kit is encased in asterile tray or other receptacle for use by an operator at a site.

The invention will be further illustrated by the following Example.

EXAMPLE

An expandable member is formed of natural high density polyethylene("PE"), type PDC 9122, supplied by Dow Chemical Co. (Dow HD8354N) anddimensioned to slide easily into a 0.138 inch (3.5 mm) diameter bonehole. The outer surface of the member is molded to a 6-32 screw threadconfiguration to provide screw threads. A 6-32 screwthread configurationprovides a 0.138 inch outermost diameter so that the member can beinserted into a 3.5 mm bone hole without resistance. The axial channelof the member is of a uniform 0.070 inch (1.8 mm) diameter, and itslength is 0.422 inches (10.3 mm).

The insertible element is formed of Dupont Delrin E 500, molded to havethe general shape shown in FIG. 4 and an outermost diameter of 0.107inch (2.7 mm). Delrin is much less deformable than the polyethylene ofwhich the expandable member is made. The proximal leading edge of theinsertion element permits the relatively incompressible element to beforced into the 0.070 inch expandable member axial channel and to expandthe relatively soft expandable member. When the insertion element hasbeen fully inserted within the expandable member, the device has anoutermost diameter approximately 0.160 inch (4.1 mm), providing forsubstantial deformation of the outer surfaces of the expandable memberinto the irregular wall of the bone hole, and thereby forming a firmfastener for the expandable member and insertion element. The elementhas an axial channel of diameter 0.046 inches (1.1 mm), which accepts apair of sutures for later use in attaching soft tissue to the bonesurface. Before insertion of the element, the sutures are passed throughthe axial channel of the insertion element and their proximal ends areknotted so that they stop against the proximal end of the insertionelement.

The outside configuration of the member is a 6-32 thread which providesa series of ridges which assist in permitting deformation of theexpandable member in the bone hole and conformation of the expandablemember outer surface as it is pressed into the 0.138 inch (3.5 mm)diameter bone hole. In this prototype, the threads are not used forturning the expandable member into the bore, but rather to facilitatedeformation of the outer portion of the member when the member isexpanded within the bone hole. When the insertion element is insertedinto the axial channel of the expandable member, the threads aredeformed by irregularities in the cancellous bone hole wall, locking thefastener, and the element compressed within it, into place.

The expandable member is formed with frangible, integral connection to acylindrical holding means as described above, enclosed within acartridge, and provided with the apparatus as described above,configured and dimensioned as follows:

The holding means, for example as shown in FIG. 24, is formed as acylinder having inside diameter of 0.145 inches (3.7 mm), outsidediameter 0.230 inches (5.8 mm), and a total length of 6.0 inches (152mm). The frangible membrane between the holding means and the expandablemember is formed as an annulus having a thickness of 0.012 inches (0.30mm).

The plunger and releasing means are constructed by turning a stainlesssteel rod to provide a punch-and-die configuration (generally as in FIG.24) having an outer diameter of 0.145 inches (3.7 mm). The severingmeans is formed by machining the end of the rod to form a sharpenedstep, located approximately 0.060 inches (1.5 mm) distal to the bluntproximal tip of the plunger.

As the plunger is pressed frontward, it presses the insertion elementbefore it into the axial channel of the expandable member, expanding itand deforming it against the bone hole wall. When the element approachesthe point where it has been pressed fully into the member, the sharpenedstep reaches the 0.012 (0.30 mm) inch thick connecting annulus andpasses through it, shearing it and separating the expandable member fromthe holding means. Then the cartridge is withdrawn together with theplunger and the holding means, leaving the fastener fixed within thepredrilled bone hole.

A 3.5 mm (0.138 inch) diameter hole is made in the bone to a depth ofabout 14 mm using a drill with a stop to limit the hole depth. Theprototype device is emplaced as described above, in femur bone recoveredfrom a pig cadaver, and then is tested as follows.

The hole is drilled into the pig femur approximately normal to the bonesurface to a depth about 14.25 mm using a step drill. Then a fastener isloaded with a pair of #2 non-sterile braided polyester sutures coupledto a hand-held means, positioned, and fixed in the bone hole asdescribed above. A knot is tied in the sutures at some distance from thefastener and looped over an Ametek Accuforce Cadet digital force gauge,0-50 lbs. range (Mansfield & Green). The slack in the sutures is takenup by drawing the force gauge by hand away from the fastener in adirection perpendicular to the bone surface. The holding force is thentested by sharply pulling the force gauge away from the bone by hand ina direction perpendicular to the bone surface. In such preliminarytests, the fastener held and the suture broke. These results demonstratea holding capacity equivalent to those shown in similar tests usingknown devices now on the market.

The fastener according to the invention provides a platform to securethe suture because it is locked into dense bone, and because theconformity of the expandable member surface with irregularities in thebone provides efficient fixation. Moreover, there are no sharp edges inthe fastener that can abrade the suture.

The bone fastener according to the invention can be used for fasteningbone to any of a variety of objects, including tissues such as ligamentsor tendons and prostheses such as bone plates. The fastener andemplacement apparatus can be used in any of a wide variety of orthopedicsurgical procedures and settings. The fastener can provide superiorholding capacity and relatively small size, and can be installedaccording to the invention without impulse, impact or hammering andwithout imposing any substantial net force toward or away from the bonesurface, and so the invention provides for fastening in surgicalsettings in which bone anchors have not been used, or have been usedwith limited success.

The fastener according to the invention is of a readily drillablematerial, and the installed fastener is situated near the bone surface.Thus, removal of the device from the bone in a later surgical procedureis straightforward. If removal of a fastener is indicated, the surgeoncan simply use a retrieval device, consisting of for example, a drillbit, preferably of a somewhat smaller diameter than the original bonehole. The drill bit can be used to excavate the insertion element andthen the anchor and any debris can be simply withdrawn from the hole.

EQUIVALENTS

It should be understood that various changes and modifications of thepreferred embodiments may be made within the scope of the invention.Thus it is intended that all matter contained in the above descriptionbe interpreted in an illustrative and not limited sense.

We claim:
 1. A fastener for coupling an object to bone comprising, an approximately cylinder shaped member of expandable material for insertion into an opening in a bone, the member including an outer surface having structure for expandable engagement with an inner surface of the bone opening, said expandable member having an axial channel defined therein extending at least partially between proximal and distal ends of said expandable member;an elongated element for insertion into said expandable member, at least a portion of the insertion element having an outer diameter greater than an inner diameter of the expandable member, whereby by insertion of said insertion element into the axial channel of said expandable member causes, the expandable member is irreversibly expanded to obtain a pressure fit with said opening in said bone.
 2. The fastener of claim 1, wherein the outer surface of the expandable member has defined therein a plurality of projections for engagement with the inner surface of the bone opening.
 3. The fastener of claim 1, wherein said distal end of said expandable member includes a means for axially releasing said expandable member from a holding means.
 4. The fastener of claim 1, wherein said channel of said insertion element extends completely between said proximal and distal ends.
 5. The fastener of claim 4, further comprising a suture engaged with an end of said insertion element.
 6. The fastener of claim 1, wherein distal end of the expandable member includes a radially-outwardly projecting portion for engagement with the object to be coupled to the bone.
 7. The fastener of claim 6, further comprising a washer having defined therein a central bore, a portion of the insertion element disposed within said bore.
 8. The fastener of claim 7, wherein said washer is adapted for movement on said insertion element.
 9. The fastener of claim 1, wherein the expandable member is formed out of a biocompatible material.
 10. The fastener of claim 1, wherein at least a portion of the insertible element is formed out of a bioabsorbable material.
 11. A fastener for coupling an object to bone comprising,an expandable member for insertion into an opening in a bone, the member including an outer surface for expandable engagement with an inner surface of the bone opening, said expandable member having an axial channel defined therein extending at least partially between proximal and distal ends thereof said expandable member comprising means for axially releasing said expandable member from a holding means; an elongated element for insertion into said expandable member; at least a portion of said elongated element having an outer diameter greater than an inner diameter of the axial channel of the expandable member for expansion thereof upon engagement therewith, whereby, by insertion of the elongated element, the expandable member is irreversibly expanded to obtain a pressure fit with said opening in said bone.
 12. The fastener of claim 11, wherein the means for axially releasing comprises at least a portion of a frangible membrane.
 13. The fastener of claim 12, wherein said insertion element includes a channel defined at least partially between said proximal and distal ends for engagement with a suture.
 14. An expandable member for use in a bone fastener, comprising a substantially cylindrical outer surface for engagement with an opening in a bone, said member having proximal and distal ends; said member having defined therein an axial channel extending at least partially between said ends and defining an inner surface of said member, said axial channel susceptible to enlargement by a compressive force acting substantially orthogonal to said inner surface of said expandable member;a plurality of projections extending radially outwardly from said outer surface for contacting the bone within said opening upon enlargement of said channel; and means engaged with said distal end of said expandable member for axially releasing said member from an elongated holder.
 15. The expandable member of claim 14, further comprising an elongated element inserted into said axial channel of said expandable member, the insertion element including proximal and distal ends, said proximal end of the insertion element having a projection engaged with an inner surface of the channel of said expandable member, said projection arranged to expand said member upon insertion into said distal end of said expandable member.
 16. A fastener for coupling an object to bone comprising,a substantially cylindrical member of expandable material for insertion into an opening in a bone, the member including an outer surface having structure for expandable engagement with an inner surface of the bone opening, said expandable member having an axial channel defined therein extending at least partially between proximal and distal ends thereof; an elongated element for insertion into said expandable member, the insertion element including a channel defined in a direction substantially orthogonal to the longitudinal axis of the element for engagement with an intermediate portion of a suture, wherein at least a portion of the insertion element includes an outer diameter greater than an inner diameter of the axial channel of the expandable member for expansion thereof upon engagement therewith, whereby, by insertion of said insertion element, the expandable member is irreversibly expanded to obtain a pressure fit with said opening in said bone.
 17. The fastener of claim 16, wherein the distal end of the expandable member further comprises means for axially releasing the expandable member from a holding means. 